Refractive surgery is a known method of treating myopia, hyperopia, astigmatism, and certain corneal abnormalities in humans. This process involves reshaping various layers of the cornea to change the refractive surface thereof. Refractive surgical methods include radial keratotomy, radial keratectomy, lamellar keratectomy, lamellar keratotomy and others. One procedure for performing laser keratectomy (reprofiling of the cornea) by laser ablation comprises removal and discarding the central epithelium and then exposing the underlying surface to the laser.
Prior art micro-keratome instruments comprise a vacuum ring, a knife blade, and an applanation shoe assembled onto the vacuum ring. The knife blade makes a single cut at the appropriate corneal depth as determined by the height of the applanation shoe. In some procedures the cut-away layer is entirely detached from the remainder of the cornea. Generally, the cut is such that the membrane layers to be removed are not completely detached from the cornea, but remain connected by a flap allowing the membrane to be folded to one side, while underlying stromal issue is removed. After cutting, the knife blade is retracted allowing the membrane to temporarily settle back to its original position. Then the superficial corneal section is hinged to one side. A second corneal incision is made removing corneal stromal tissue from the underlying bed. The superficial corneal section is then folded back into its original position.
Prior art micro-keratome instruments require a transverse oscillatory cutting motion be used to insure accurate cutting of the cornea, and to prevent deforming or bunching of the corneal membranes during cutting. These complex cutting motions are a result of the steel blades used in conventional devices. Additionally, the steel blades have limited life spans and require regular replacement.
Conventional cutting devices stabilize the globe by vacuum-mounting the keratome to the globe. However, prior to making the second corneal incision to excise corneal tissue from the underlying corneal bed, the cutting device must be removed. The vacuum ring may remain on the eye after removing the cutting device in some surgical procedures. Hence, the vacuum-induced globe stabilization is terminated. With the globe in this state, the corneal flap created by cutting can be manually folded away. Hence, damage to the flap could occur during this time. Moreover, the delay encountered by removing the cutting apparatus can result in changes in hydration of the corneal flap during apparatus removal. This may also result in epithelial cells being deposited in the interface. The corneal flaps are difficult to reset into the original position. Such repositioning is even more difficult in those procedures wherein the lamellar incision removes an entire area of the cornea (no connecting area) which is removed in the form of a corneal cap.